When sampling phrases I'd prefer to sample from movie soundtracks and also the soundtracks from before '90. Old stuff anyway but from good producers such as Morricone and Mancini. I don't feel doing something wrong here since the application is to another musical platform. The movie soundtracks had no intentions for anything else than the movie so applying phrases for hiphop purpose is at least original use of the material. Now, when talking about sampling more recent stuff or material from bands or artist, non instrumental tracks or tracks that were made for exploitation of the producer himself, is something I'd disagree with and is also not very original. Those phrases are too much recognisable and for that reason the exploit and rights belong to the originator, so if you're "remixing" ( read sampling ) you should pay those rights. I do sample from bands, artist but again, these are mostly old productions and not recent productions, just like the movie soundtracks and preferably blaxploitation music. If any of those tracks would appear a lucrative production than I would surely pay the material and since I listen to music with great pleasure I wouldn't mind at all and pay my credits to the originator.
For short samples like a sliced drumsamplekit from Booker T & the MG's track I dont bother about the rights since the sliced drumhits are too small of a sample to clear and second, who the fug is going to recognise it when I finished the track ??? I mean, some stuff is to be recognised since they're been used a zillion times, I have a lot of em on my SC page and if you fail to hear then you're missing out on some knowledge of classic drumloops. But, since there are a zillion tracks to be found that have usefull drumsections, you'll find enough material which is highly original material and the outcome of such material on a track depends on the one who's gonna use it for a beat in order to decide if anyone could recognise it.
So, concluding myself, it all depends on how original you want to be. If you do less on editing the samples then people will hear something familiar and if you pay attention on it than nobody will hear.